In the film, Gordon-Levitt, 31, plays an assassin who’s hired out to kill victims sent through a time machine, only to find that he’s latest target is actually his future self (played by 57-year-old Willis).

Celebuzz caught up with the actor — and his costar Emily Blunt — at San Diego’s Comic-Con where the star spilled on how he prepared for the part.

“I didn’t work out at all,” he told Celebuzz. “But I did just do a part where I worked out.”

How does Gordon-Levitt — who’s starred in action-thrillers like Inception and The Dark Knight Rises — bulk up for a role?